1. Field of the Invention
The present invention relates to Auger electron spectroscopy and an apparatus thereof, which applies an energetic quanta to a substance to achieve elemental analysis of the surface and a very thin surface layer of the substance and analysis of the surface condition from electrons emitted by an Auger process.
2. Description of the Prior Art
As is well known, when an atom of an element having more than one electron orbit is applied with an external energy exceeding a predetermined threshold value, some of the electrons in the stable orbit are ejected out from the inside orbit. There occurs a phenomenon in which, to supply electron holes generated by such ejection of electrons, an electron in the outer orbit moves to the hole, and other electrons in the outer orbit are emitted. Such an emitted electron is called an Auger electron, which has a specific energy, and its energy differs for different elements. Therefore, the energy of the emitted Auger electron can be measured to analyze the element emitting the electron.
As described above, the energy of an electron emitted from the surface of a substance by the Auger process has a value which is specific to each element, and varies slightly with the bonding condition of the element. Therefore, the energy and intensity of an Auger electron emitted from a substance can be measured to achieve an elemental an analysis of the surface and analysis of surface condition of the substance.
As previously described, to effect the Auger process, it is necessary to make vacant the energy level of the inner shell of electron orbits of the element. To achieve this, the element has heretofore had applied thereto an energy exceeding a predetermined threshold value. High energy electrons, high energy ions, and high-energy photons have such an energy. An inner shell electron is excited by such an energetic quantum to generate a hole in the orbit. Recently, on the other hand, it has been proposed to use positrons, which are antiparticles of electrons, as a method for creating an electron hole in the inner electron orbit of a sample element. The positron, when applied to an element, collides with an inner shell electron of the element and is annihilated with the electron to create a hole in the inner orbit.
A positron-induced Auger electron spectroscopy and apparatus have the following advantages over Auger electron spectroscopy and apparatus using other energetic quanta.
(1) Since the energy of an incident positron can be lower than that of the Auger electron, in an energy spectrum, background noise due to electrons other than the Auger electron at a peak position of the Auger electron can be reduced.
(2) Since the energy of the incident positron can be reduced, the implantation depth of the positron can be reduced and, furthermore, a positron reaching a position slightly inside the surface has a high probability of reverting back to the surface where it annihilated with an electron of the outermost atom, thereby providing a very high surface sensitivity.
(3) Since this technique is low in background noise and high in surface sensitivity, the amount of the incident beam can be reduced, thereby reducing damage to the sample surface.
Heretofore, as a positron-annihilation-induced Auger electron spectroscopic apparatus, one which is shown in FIG. 1 has been known (e.g. Physical Review B, vol. 42, No. 4, p.1881).
Hereinafter, e.sup.+ is referred to a positron or positron beam, and e.sup.- is referred to an Auger electron or Auger electron beam.
In FIG. 1, symbol 11 indicates a positron generator for generating a positron beam e.sup.+, symbol 2 indicates a sample, symbol 31 indicates a position-sensitive electron detector, symbol 5 indicates a deflection electrode for beam orbit separation, symbol 6 indicates a magnet such as a permanent magnet or an electromagnet, and symbol 7 indicates a deflection electrode for energy analysis. The entire apparatus is contained in a vacuum vessel.
In these apparatuses, a positron beam e.sup.+ is guided by a magnetic field B to the sample 2, where the positron e.sup.+ collides with and annihilates an inner shell electron in the sample 2 to create a hole in the inner shell electron orbit. The emission direction of Auger electron e.sup.+ emitted by transition of an outer shell electron into the hole is arranged by the magnet 6, separated from the orbit of positron e.sup.+ by the deflection electrode 7, and the energy of the Auger electron e.sup.- is analyzed by an energy analyzer comprising the deflection electrode 7 and the position-sensitive electron detector 31.
In the prior art apparatus shown in FIG. 1, since the energy analysis uses the deflection electrode 7 and the position-sensitive electron detector 31, and the positron beam e.sup.+ incident to the sample 2 has a spatial spread, it has been difficult to analyze the energy with a high resolution. Therefore, there have been problems in that elements having energy distributions which are close to each other cannot be distinguished, and minute changes in peak positions cannot be measured.
With a view toward eliminating the above-described prior art problems, it is a primary object of the present invention to provide a position-induced Auger electron spectroscopy and an apparatus therefor which can conduct Auger electron spectroscopic measurement using a positron beam, and which features low background noise and high surface sensitivity with high resolution.